Developments in sensor technology, such as the use of microelectromechanical systems (MEMS), have enabled the incorporation of a wide variety of sensors into mobile devices. Non-limiting examples of such sensors include an accelerometer, a gyroscope, a magnetometer, a pressure sensor, a microphone, a proximity sensor, an ambient light sensor, an infrared sensor, and the like. One or more of these sensors, or others, may be used for a similarly wide variety of purposes, including monitoring, characterizing or analyzing quantities related to the health of a user. As an illustrative example only and without limitation, a health sensor may be a photoplethysmograph used to determine the pulse rate and/or blood oxygen saturation of a user by sensing changes in the amount of light absorbed by tissue. Accordingly, the quality of the data provided by the photoplethysmograph may depend on how securely the sensor is engaged with the user, otherwise movement of the sensor with respect to the user may produce erroneous signal components, such as may be attributed to varying amounts of ambient light being recorded. It should be appreciated that many other types of sensors may also be influenced by how a portable device incorporating them are associated with a platform, such as a user.
In light of these observations, it would be desirable to assess one or more characteristics of the association between a user and a portable device. For example, it would be desirable to determine whether a wearable device is engaged with a user, allowing the data being output by the sensor to be interpreted more accurately. Further, it would be desirable to validate data output by a sensor when it is determined the wearable device is engaged with the user. Still further, it would be desirable to utilize different algorithms or otherwise adjust the analysis of sensor data depending on whether the wearable device is engaged with the user or not. More generally, it would be desirable to use the determination of the engagement of any portable device with a platform when using sensor data, such as for aiding a navigational solution that uses motion sensor data provided by the portable device. The techniques of this disclosure satisfy these and other needs as described in the following materials. While the following discussion is in the context of MEMS sensors as used in portable devices, one of skill in the art will recognize that these techniques may be employed to any suitable sensor application as desired.